What It Is:

: a heavy catapult used in ancient and medieval times

About the Word:

Onager has an ancestor in the Greek onos, meaning "ass." That term developed into both the four-legged onager (an Asian wild ass) and the wooden onager (the catapult).

Like its animal namesake, the catapult onager had a tendency to kick up its rear end – though the catapult only did this when its stone was discharged.